1985 Mercury Black Max oil alarm >3k RPM

Hi all. Working on a ~1985 Mercury Black Max 175 that was in storage for 12 years. I’m told by the owner that it was completely overhauled shortly before going into storage, and he wants to keep everything as is as much as possible. I know deleting the oil injection and running premix is popular, but that’s not what he wants to do since everything was replaced, so please don’t just suggest that.

With that out of the way, I have the motor running fine except getting an oil alarm (beep beep beep, not constant tone) over 3000 RPM or so. Things we've done/tried/tested since pulling out of storage:

• Compression checks good, bore scoped cylinders
• New fuel lines and rebuilt fuel pump
• New plugs, coils, and spark plug wires
• New impeller/water pump and thermostat
• Oil reservoir cap checks good
• Oil pump flow rate checks good per service manual
• Checked oil pump drive gear and driven gear on crank with borescope
• Oil pump rotation sensor and oil cap checks good
• New warning module
• Swapped green wire from warning module to multiple cylinders
• Trigger impedance checks good
• Stator impedance is not within spec

Engine starts and runs fine at all RPMs. It smokes a bit, smells like a 2 stroke, etc. It is getting oil. Below 3k RPM, it'll run all day with no alarm. Alarm starts quickly over 3k RPM. Once the alarm starts, it will not stop until the motor is shut off. The alarm will not sound when the oil pump rotation sensor is unplugged. But it is rotating and pumping oil at the rate it's supposed to and giving the proper 5V pulse. The magnet is encased in the coupler between the pump and drive shaft, there’s no way for it to fall out or be in backwards.

I have a DVA on the way to check the stator output since the warning module compares signal from that to the rotation sensor to make sure the pump is rotating with the engine. Was thinking maybe the high speed coils are not quite up to spec. Doing a simple impedance check, the stator is not within spec.

Any ideas what could be causing this? Am I on the right track with the stator potentially? Or what about a switchbox? Again, I want to find the actual answer here, not just delete and premix per owner's desire.

Thanks!

One thing I forgot to mention, I'm 99% sure it checked out ok when installed but last time I checked the white wire on the alarm module that's supposed to be 12v was 5v, so I guess the alarm module could be an issue as well. I've been thinking it will end up being the high speed side of the stator but the motor runs fine at 5k+ RPM so I'm not sure. I'll be checking with DVA. Does anyone know the tolerance for the alarm module green wire for the ignition beyond which it will trigger the alarm if out of spec? Or have any other thoughts on this problem?

I've been using a factory service manual I found online for 1992+ motors since like 95% of things are the same as this motor, but I've noticed when looking at specific part number versions, the stator is one of the things that isn't the same. My manual references a 40 amp stator, and this motor has either a 9 or 15 amp. How can I tell which it is and what should the DVA specs be? The owner has an appropriate year Seloc manual that I've been referencing also but it doesn't list DVA specs.

The serial number of the motor is 6619576. Any help identifying which stator it has, what kind of ignition voltage it should be putting out, and what voltage it should be charging the battery at would be very helpful.

Actually, the early Merc V6 motors had the low amperage stators, usually with unregulated charging systems and full wave rectifiers. Merc then went to a single 40A stator/VR, and finally (by 1993) the V6 Mercs had twin 20A Stator coils and VRs.

I do not think the stator is your issue, however, I am not familiar with the oil injection system.

Yeah, looking at the factory parts diagram for the serial number range that covers this motor, it lists 3 potential options. Not sure which one this is and what I should be testing for. I agree it's looking less like this is the problem but now I have the DVA so want to test it either way.

If anyone has any ideas about the alarm problem, that'd be even better.

your motor has a 16 amp system with separate reg and rectifier.. tha 40 amp stuff started in '89 with a single water cooled reg/rect... that changed to tha two 20 amp reg/rect in '92...
tha oiler information pretty much remains tha same thru all tha years up until '02.....

tha oiler module gets its power from tha purple (switched power) wire.. should be 12v when key is turned on..
tha "rotation" sensor alarm mode is hit or miss at its best.. some work fine and some don't.. why that is i haven't a clue but its jus tha way they are...

Ok thanks. And yeah the oil injection stuff is what I've been focused on and looked like the same for many years.

For the charging system on this motor, should I be seeing >14v at the battery when it's running or will it just be a bit over 12 since it's the 16a not the newer 40amp system?

The alarm module is getting 12v from the purple wire, but last I checked it wasn't putting out 12v to the rotation sensor like it's supposed to. I should be able to test that with a jumper though, right? Feed it 12v from the hot wire to make sure it's not just that that's the problem?

my experience with tha module is very limited.. i can't remember any motor i've had that we retained a functioning oiler.. not because of failure of tha oiler it was because we usually had "0" knowledge of tha motors "TRUE" past.. ie: hours, how it was maintained, ever been over heated etc... you could take "they say" with tha grain a salt!